1. Field of the Invention
The present invention relates to a fiber reinforced thermoplastic resin structure controlled in the degree of combing of the reinforcing fibers and fiber length and superior in shapeability (or moldability), mechanical properties, and surface smoothness, a process for production of the same having a high productivity, and an apparatus for production of the same. More particularly, it relates to fiber reinforced thermoplastic resin pellets suitable for making automobile cylinder head covers, bumper beams, seat frames, instrument panels, wheel caps, battery trays, etc., office automation equipment and home appliance chassis, housings, etc., and further tool housings and fiber reinforced thermoplastic sheets suited for extrudates, blow molded products, tubes, pipes, and sheets, and further hot molding use sheets.
2. Description of the Related Art
Fiber reinforced thermoplastic resin structures are used for various types of applications, such as auto parts and parts for office automation equipment, making use of their superior mechanical properties. In particular, studies are underway for increasing the length of the reinforcing fibers so as to improve the mechanical properties etc. For example, in the case of fiber reinforced thermoplastic pellets, as shown in Japanese Examined Patent Publication (Kokoku) No. 41-20738, in a method for extruding a chopped strand using an extruder, the reinforcing fibers end up breaking and therefore good mechanical properties cannot be exhibited. Accordingly, studies have been pursued so as to increase the fiber length of the reinforcing fibers so as to improve the mechanical properties etc. As shown in Japanese Examined Patent Publication (Kokoku) No. 63-37694, a roving of reinforcing fiber connected by the pultrusion method is covered with a plastic and cut into predetermined lengths to form pellets. Further, there are also known pellets with uniformly dispersed reinforcing fibers of a fiber length of 3 to 20 mm obtained by the paper machine process and the dry nonwoven fabric process as shown in Japanese Unexamined Patent Publication (Kokai) No. 3-7307 and pellets obtained by mixing a resin powder and glass fibers in advance in a Henschel mixer etc. and then melting in a ram extruder as shown in Japanese Unexamined Patent Publication (Kokai) No. 63-9511. Further, in the case of thermoformable sheets, there are known sheets obtained by the laminate method of sandwiching in a glass fiber mat between thermoplastic resin sheets such as shown in Japanese Examined Patent Publication (Kokoku) No. 63-15135, sheets obtained by the paper making machine process including discontinuous filaments of 7 to 50 mm length such as shown in Japanese Examined Patent Publication (Kokoku) No. 4-40372, the process for obtaining thermoplastic resin sheets by mixing thermoplastic resin powder and reinforcing fibers under a jet of air, causing the mixture to accumulate on a conveyor belt to transport the same and at the same time heating and pressurizing the same to melt the thermoplastic resin such as shown in Japanese Unexamined Patent Publication (Kokai) No. 59-49929 and Japanese Unexamined Patent Publication (Kokai) No. 62-208914, and a thermoplastic resin sheet obtained by the method of introducing thermoplastic resin and a web-like material of glass fibers of 3 to 100 mm length into an extruder and feeding the same into a melt extrusion die to form a web sheet such as shown in Japanese Unexamined Patent Publication (Kokai) No. 2-235613.
Further, as the method for feeding a continuous roving into an extruder, there is known the method of placing the glass fibers into the melt in a screw extruder in the form of a braid and cutting it into suitable lengths such as shown in Japanese Examined Patent Publication (Kokoku) No. 44-16793. Further, as attempts to control the degree of combing and fiber length of reinforcing fibers by an extruder, there are known the process of supplying a glass roving from the second supply port of a twin-screw extruder to separate it into filaments such as in Japanese Unexamined Patent Publication (Kokai) No. 58-56818, a reinforced material such as shown in Japanese Unexamined Patent Publication (Kokai) No. 60-221460, a material dispersed with short fibers cut in the kneading apparatus such as shown in Japanese Unexamined Patent Publication (Kokai) No. 4-125110, and the process of kneading using piston motion such as shown in Japanese Examined Patent Publication (Kokoku) No. 4-80810. Further, as an extruder with a processed screw or cylinder, there are known screws provided with combing and kneading regions having large numbers of projections for grinding down organic fillers such as shown in Japanese Examined Patent Publication (Kokoku) No. 62-57491, screws of barrier type mixing sections roughened to crush the inorganic matter, additives, etc. such as shown in Japanese Examined Patent Publication (Kokoku) No. 63-56845, and kneading elements composed of specially processed cylinders or screws for kneading thermoplastic resins such as shown in Japanese Examined Patent Publication (Kokoku) No. 60-8934.
However, in the above structures, while the reinforcing fibers become longer in length, their degree of combing and kneading action are insufficient, and therefore, not only are the fluidity and mechanical properties insufficient, but also the productivity thereof is low. In particular, pellets obtained by the pultrusion process and pellets obtained by the process of Japanese Examined Patent Publication (Kokoku) No. 44-16793 contain fibers of long fiber length, but the degree of combing of the fibers is also poor, so when press formed, the plastic and fibers end up separating or the fluidity at the time of injection molding is poor. Further, in the case of the paper-machine process, while there is no fiber breakage and uniform shaped articles with fibers dispersed down to the filament level are obtained, the kneading action is small, so the bonding strength at the interface of the plastic and reinforcing fibers is low and the mechanical properties are inferior. Further, the glass mat laminate process gives superior mechanical properties, but the fluidity is poor at the time of press forming and other hot molding and the fiber does not flow to the corner portions etc. Therefore, there has been a demand for a fiber reinforced thermoplastic resin structure controlled in degree of combing and fiber length of the reinforcing fibers, superior in fluidity, mechanical properties, and surface smoothness, and high in productivity.
In general, use of an extruder enables high productivity, but in the processes of Japanese Unexamined Patent Publication (Kokai) No. 58-56818, Japanese Unexamined Patent Publication (Kokai) No. 60-221460, Japanese Unexamined Patent Publication (Kokai) No. 4-125110, and Japanese Examined Patent Publication (Kokoku) No. 4-80810, the degree of combing and fiber length of the reinforcing fibers could not be sufficiently controlled and when the kneading action of the screw was strengthened, the fiber length ended up becoming shorter and the mechanical properties falling. If the kneading was made weaker, the degree of combing became insufficient and the reinforcing fibers nonhomogeneous. Further, Japanese Examined Patent Publication (Kokoku) No. 62-57491, Japanese Examined Patent Publication (Kokoku) No. 63-56845, and Japanese Examined Patent Publication (Kokoku) No. 60-8934 merely ground down the inorganic or organic fillers and kneaded the thermoplastic resins, so could not control the degree of combing and fiber length of the reinforcing fibers.
Accordingly, the object of the present invention is to provide a fiber reinforced thermoplastic resin structure which is superior in fluidity, mechanical properties, surface smoothness by dispersing the reinforcing fibers uniformly in the thermoplastic resin to achieve a specific distribution of fiber lengths while keeping the weight average fiber length long.
Another object of the present invention is to provide a fiber reinforced thermoplastic resin structure which is superior in fluidity, mechanical properties, surface smoothness, etc. by providing a fiber reinforced thermoplastic resin structure which is controlled in its degree of combing and has reinforcing fibers uniformly dispersed throughout it and which is given a specific distribution of fiber length by a kneading action while maintaining the weight average fiber length long.
A further object of the present invention is to provide a fiber reinforced thermoplastic resin structure which is superior in fluidity, mechanical properties, surface smoothness, etc. by providing a fiber reinforced thermoplastic resin structure of sheets or pellets which are combed to a high degree, have a long weight average fiber length, and have a specific distribution of fiber length.
A further object of the present invention is to provide a process for production of a fiber reinforced thermoplastic resin structure superior in fluidity and mechanical properties by controlling the degree of combing and/or fiber length of the reinforcing fibers by melt extrusion of the thermoplastic resin and continuous roving by an extruder having a specific construction.
A still further object of the present invention is to provide an extruder capable of providing a fiber reinforced thermoplastic resin structure superior in fluidity and mechanical properties by controlling the degree of combing, weight average fiber length, or fiber length of supplied continuous fibers.
That is, to achieve the objects of the present invention, there is provided a fiber reinforced plastic structure including reinforcing fibers, which fiber reinforced plastic structure is characterized in that the ratio (Lw/Ln) of the number average fiber length (Ln) to the weight average fiber length (Lw) of the reinforcing fibers uniformly dispersed in the structure is from 1.1 to 5 and the weight average fiber length is from 1.0 mm to 200 mm.
Further, the present invention provides a process for production of a fiber reinforced thermoplastic resin structure by melt extrusion of the thermoplastic resin and continuous roving by an extruder, which process for production of a fiber reinforced thermoplastic resin structure is characterized in that the degree of combing and/or fiber length of the reinforcing fibers in the plastic matrix are controlled by the combing action of irregularly shaped processed surfaces by passing the melted thermoplastic resin and reinforcing fibers through a control mechanism formed by processing of a screw and/or cylinder to make its surface irregular at least at part of the screw surface and/or cylinder inner wall and provides an extruder for production of a fiber reinforced thermoplastic resin structure provided with a screw and cylinder, which extruder for production of a fiber reinforced thermoplastic resin structure is provided with a control mechanism formed by processing a screw and/or cylinder to have irregularly shaped processed surfaces enabling control of the degree of combing and fiber length by combing the supplied continuous roving.
Further, there is provided one of the above-mentioned extruders characterized by correcting the spiral flow caused by the extruder screw by attaching one or more plates in the cylinder of the extruder between the front end of the screw and the die. When the fiber reinforced thermoplastic resin structure is a pellet, to prevent breakage of the reinforcing fibers at the die portion during stranding during production of the fiber reinforced thermoplastic resin pellets, provision is made of a die assembly which is attached to the front end of the extruder directly or via an adaptor and which is thermoplastic resin plates of a predetermined thickness formed with a plurality of through holes, which die has through holes of a frustoconical shape, which has a value of R/r greater than 1 when the radius of the circle formed by a through hole at the extruder side and the discharge section side are R and r, respectively, which circles formed by the through holes at the extruder side covering at least 90% of the front end of the extruder to which the die is provided or the discharge sectional area of the adaptor.